Olefin metathesis is an indispensable tool in making carbon-carbon bonds in modern organic synthesis. For recent reviews, see, e.g., (a) Grubbs, R. H. Handbook of metathesis; Wiley-VCH: Weinheim, Germany, 2003; (b) Hoveyda, A. H.; Zhugralin, A. R. Nature 2007, 450, 243-251; (c) Schrodi, Y.; Pederson, R. L. Aidrichimica Acta 2007, 40, 45-52; (d) Grubbs, R. H. Tetrahedron 2004, 60, 7117-7140; (e) Furstner, A. Angew. Chem., Int. Ed. 2000, 39, 3013-3043; (f) Nicolaou, K. C.; Bulger, P. G.; Sarlah, D. Angew. Chem., Int. Ed. 2005, 44, 4490-4527. Since the development of well-defined ruthenium-based metathesis catalysts, there has been significant effort directed towards improving the catalyst efficiency. Most notably, the substitution of a phosphine ligand of RuCl2(PCy3)2(═CHC6H5) for a bulky, electron-rich N-heterocyclic carbene (NHC) ligand led to metathesis catalysts with enhanced reactivity and stability. See, e.g., (a) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953-956; (b) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118, 100-110; (c) Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 1995, 34, 2039-2041. the high reactivity of NHC complexes is often attributed to the superior electron donor ability of NHC ligands in comparison to the phosphine ligands. See, e.g., (a) Sussner, M. S.; Plenio, H. Chem. Comm. 2005, 5417-5419. (b) Hadei, N.; Kantchev, E. A. B.; O'Brien, C. J.; Organ, M. G. Org. Lett. 2005, 7, 1991-1994.)
In addition, the use of NHC ligand has allowed access to metathesis catalysts suitable for various applications through the modification of NHC ligand, such as water-soluble metathesis catalysts, solid-supported catalysts, and highly active catalysts suitable for hindered substrate. See, e.g., (a) Deshmukh, P. H.; Blechert, S. Dalton Trans. 2007, 2479-2491 and references therein; (b) Stewart, I. C.; Douglas, C. J.; Grubbs, R. H. Org. Lett. 2008, 10, 441-444; (c) Stewart, I. C.; Ung, T.; Pletnev, A. A.; Berlin, J. M.; Grubbs, R. H.; Schrodi, Y. Org. Lett. 2007, 9, 1589-1592.)
Although a variety of metathesis catalysts are available to address a range of problems in chemistry, it is still a challenge to obtain more robust catalysts that can be reliably applied in industrial processes. Ruthenium NHC complexes, albeit significantly more stable than the corresponding bisphosphine complexes, have limited lifetime. Recent catalyst stability studies suggested that C—H activation within the catalyst framework is responsible for the decomposition of the active ruthenium complexes. For instance, the X-ray structure of thermally degraded of ruthenium complexes bearing N-mesityl or N-phenyl-substituted NHC ligand revealed that the N-aryl substituents of NHC ligand have been altered by the metal center (Compounds C1-5 below). See, e.g., (a) Hong, S. H.; Wenzel, A. G.; Salguero, T. T.; Day, M. W.; Grubbs, R. H., J. Am. Chem. Soc. 2007, 129, 7961-7968. (b) Hong, S. H.; Chlenov, A.; Day, M. W.; Grubbs, R. H., Angew. Chem., Int. Ed. 2007, 46, 5148-5151. (c) Trnka, T. M.; Morgan, J. P.; Sanford, M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T. L.; Ding, S.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546-2558. (d) Vehlow, K.; Gessler, S.; Blechert, S. Angew. Chem., Int. Ed. 2007, 46, 8082-8085.

To resolve the above issue, this invention discloses further development of efficient and stable metathesis catalysts based on ruthenium NHC complexes.